Purification of valuable hydrocarbons



Patented Sept. 23, 1941 PURIFICATION OF VALUABLE HYDBOCABBONS Frank J. Soday, Upper Darby, Pa assig'nor to The United Gaslmprovement Company, a corporatlon of Pennsylvania No Drawing. Application June Serial No. 211,945

' 8 Claims.

This invention pertains generally to the purification of hydrocarbons, and pertains particularly to the purification of resin-forming unsaturated hydrocarbons obtained from ..(l) gas condensates and tar oils produced in the manufacture of artificial gas; (2) cracked petroleum products; (3). coal tar distillates; and (4) synthetic sources such as processes tor the manufacture of synthetic styrene.

The invention pertains more particularly to the purification of crude fractions of resin-forming unsaturated. hydrocarbons derived from light oil such as crude styrene, crude indene, crude methyl styrenes, crude cyclopentadiene, isobutylene, isoprene, butadiene, piperylene, and. .the like.

In the various processes for themanufacture of artificial gas such as oil gas, carburetted water gas, or coal gas, considerable quantities of tar are produced, and the gas contains substantial quantitles of other readily condensible materials.

The latter condensates as well as the distillate from the tar are known generally as light oil and are sources for many resin-forming unsaturated hydrocarbons such. as indene, styrene, methyl styrene, cyclopentadiene, isobutylene, isoprene, piperylene, butadiene, etc.

with ordinary methods of fractional distillation as now practiced, it'is impossible to separate the resin-forming unsaturated hydrocarbons in a substantially pure state because .of the presence of other materials which apparently are either of similar boiling point or are capable of forming azeotropic .mixtures with the desired hydrocarbon. Furthermore, many of these materials are polymerizable with heat which adds to distillation dimculties.

For instance, a typical styrene fraction ob tained by ordinary distillation processes will contain hardly more than 50% styrene, and a typical indene fraction will ,contain hardly more than 80% indene. i

Such fractions as .well as those of lower and higher concentration are generally suitable for the manufacture of synthetic resins by polymerization, except that the resulting resins are very often too inferior with respect to color, color stability, electrical resistance, molding properties,

freedom from cra'zing, thermal stability, melting point, specific viscosity, molecular weight and mechanical strength as to be of any considerable value.

I find that these deficiencies are generally traceable to the presence during the polymerization of certain contaminating materials.

While I have not as yet exactly determined the character of these impurities, experimental evidence indicates that they may be classified in certain specific groups.

For example, a typical styrene fraction 0 tained from light oil was analyzed and found to contain approximately 0.1% sulfur. This indicates that crude styrene fractions obtained from, the above sources contain a relatively large quantity of sulfur containing materials such as mercaptans, disulfides, or derivatives of thiophene and related compounds.

Another portion was treated with a mercurating solution which resulted in the production of aicopious precipitate. Precipitates obtained with different portions of the starting material varied in color from a faint yellow to a light brown. This indicates, among other things, the presence of superaromatic compounds such as substituted thiophene and thiophene homologues.

The treatment of various light oil fractions with ammoniacal cuprous chloride resulted in the formation of a heavy yellow precipitate. This indicates the presence of acetylenic compounds such as phenyl acetylene.

Similar tests made with pure styrene diluted with xylene to the same concentration as the crude styrene fractions treated above gave results which were negative in each case.

Other types of impurities are doubtless present also, although specific tests have not as yet been devisedfor their detection. Among these types of impurities may be included oxygenated compounds, organic peroxides and oxides, or-

ganic per acids, aldehydes, amines, and other rethat they may act (1) as accelerators resulting grade of polystyrene; (2) as inhibitors reducin the quantity of polystyrene obtained under normal polymerizin conditions; and/or (3) they may take part in the reaction and become an integral part of the resin molecule.

The presence of contaminating impurities in the polymer molecule would undoubtedly weaken it, causing the resin to be less stable to heat and to readily decompose with the formation of undesiredcolor bodies.

The highly reactive nature of the resin-forming unsaturated hydrocarbons makes it extremely difllcult to remove the contaminating impurities.

For instance, customary methods for the removal of impurities, such as sulfur compounds,

' diolefines and acetylenes, from cracked distillates in the manufacture of motor fuels removes most, if' not all, of any styrene present.

It seems probable that any material whichis sufilciently reactive to be capable of use for the purification of the crude resin-forming unsaturated hydrocarbons will also react with them.

I have found, however, that, by a proper choice of conditions, such as temperature, time of contact, method of application and so forth, the various reactions may be made to take place at different rates with the result that practically all of the undesired contaminating materials may be removed without a considerable loss in the desired hydrocarbon.

I have also found that, although phosphoric 2 A 500 cubic centimeter (444.8 grams) sample of a typical crude styrene cut obtained from the fractionation of light oil and containing 33.3 grams of styrene per 100 cubic centimeters was agitated for 5 minutes with cubic centimeters of an 85% solution of phosphoric acid (HaPO at a temperature of C; The mixture was then allowed to stand for 5 minutes during which time a sludge settled out and was removed.

An additional 10 cubic centimeters of said 85% solution of phosphoric acid was then added and the mixture again agitated for 5 minutes. After a settling time of 5 minutes sludge was again removed.

The sample was then treated with 10 cubic centimeters of a 20% aqueous solution of sodium hydroxide with moderate stirring. After permitting the materials to settle the aqueous layer was removed.

The sample was now washed ten successive times with 10 cubic centimeters of water. The last washings were neutral to litmus which indicated complete removal of acid and alkaline residues.

The total treating loss up to this point was I only 0.9% by weight of the starting material.

uum.

This occasioned an additional loss of 1.0% of the original charge.

\ The crude styrene was now ready for polymerization.

It is to be noted that despite the reactive nature of the material being treated the total treating loss was only 3.5% by weight of the starting material, or 6.3% by weight of the styrene contained in the starting material. Most of these losses were of a mechanical nature and are, therefore, susceptible to considerable reduction, particularly in large scale operations.

The refined styrene solution had a color on the well known Gardner color scale of 1.5 as compared to a color of 25 shown by the starting material.

A sample of the refined styrene solution was subjected to polymerization for 4 days at a temperature of 145 C. in a nitrogen atmosphere.

The resin yield was 33 grams per 100 cubic centimeters of refined solution. The starting material itself contained only 33.3 grams of styrene per 100 cubic centimeters of crude solution.

Another sample of the refined styrene solution and a sample of the starting material were each subjected to identical polymerizing conditions, namely heating for a 10 day period at 100 C. in an atmosphere of nitrogen.

The resin obtained from the refined material had a color of 1.0 on the Gardner color scale, whereas the resin obtained from the unrefined material had a color of 2.0 on the Gardner color scale.

A sample of each portion of resin was subjected to molding at a temperature of 200 C. anda pressure of 2000 pounds per square inch. The molded refined material had a color of,1.1 on the Gardner color scale whereas the molded unrefined material had a color of 2.4 on the Gardner color scale.

Furthermore, the refined resin possesses unusual color stability as shown by the following test.

,A sample of resin. obtained from the refined material and a sample of resin obtained from the unrefined material were each heated for 2 days of nitrogen at a temperature siderably improved. and that it is more uniform in texture and appearance.

' Example II A 500 cubic centimeter sample (444.8 grams) of a crude styrene cut obtained by the fractionation of light oil and containing 33.3 grams of styrene per cubic centimeters was agitated for 5 minutes with 20 cubic centimeters of a 50% solution of phosphoric acid (HaPOt) at a temperature of 20 C.

The mixture was permitted to stand for 5 minutes after which time a sludge layer was removed.

The foregoing treatment was then repeated.

The sample was then treated with a 10 cubic centimeter portion of a 20 %-aqueous solution of sodium hydroxide with moderate stirring. When stirring was stopped the aqueous layer was removed.

The sample was then washed with ten successive cubic .centimeter portions of water, whereupon the refined material was dried over anhydrous sodium sulfate and distilled under vacuum.

The losses incidental to washing, drying and distilling were 1.5%, 2.5% and 1.2% respectively, making a total treating loss of 5.2%, or 11.4% of the total styrene contained in the starting material.

The refined crude styrene had a color of 1.5 on the Gardner color scale. whereas the starting material had a color of 2.5 on the Gardner color scale.

Resin obtained upon polymerization of the refined material for a period of 10 days at 145 C. in an atmosphere of nitrogen had a color of 1.5 on the Gardner color scale and a'melting point of 160 C.

Resin obtained upon polymerization of the starting material under identical conditions had a color of 2.0 on the Gardner color scale and a melting point of 154 C.

' phosphoric acid of at least 50% strength, and up to and including 100% strength.

I find that solutions of-phosphoric acid of 60% to 90% concentration are very satisfactory.

Although any suitable proportion of phosphoric acid maybe employed, I prefer to use from 0.2% to 50% by volume based upon the material being treated.

I find that from 2% to 10% of phosphoric acid by volume of the material under treatment gives very satisfactory results.

If desired suitable additions may be made to the phosphoric acid employed.

Examples of materials which might be added to phosphoric acid are (l) retarding agents, which have for their specific purpose the reduction of the effect of the acid upon the olefines. dioleflnes, and aromatic hydrocarbons present in the fraction, such as boric acid and other compounds of boron; (2) oxidizing agents, whose function is to increase th refining action of the phosphoric acid, such as KMnO4, NaMnO4, K2CI207, KCrO4, Na2C1'207, NaCrO4, chromic acid, ferric oxide, lead oxide, and the like; (3) reducing agents,the function of which is to remove highly reactive impurities by means of nascent hydrogen, such as zinc dust, iron filings, aluminum powder, magnesium powder, tin dust, nickel powder, and cadmium powder; and (4) inhibitors, the function of which is to inhibit the polymerization of the unsaturated hydrocarbons during the treating process, such as p-tertiary butyl catechol, 2-4 diaminophenol dihydrochloride, 2-amino-5 hydroxytoluene, p-benzyl aminophenol, 2-nitroso-B naphthol.

Any combination of (1), (2), (3), and.(4) may be employed except that in most cases (2) and (3) would not be added together since one tends to neutralize the other.

Acid mixtures of which phosphoric acid is one of the constituents may be used with excellent results. Examples of acids which may be mixed with phosphoric acid are sulfuric acid, acetic acid,

and sulfonic acids such as benzene sulfonic acid, toluene suli'onic acid, xylene sulfonic acid, ethyl benzene sulfonic acid, etc.

While any suitable temperatures may be employed during the various treating steps, I prefer to maintain the temperature between 40 C. and C. Temperatures between approximately -10 C. and 30 C. are very satisfactory, In general the temperature should decrease with increase in concentration of acid or other reagent to avoid any considerable permanent discoloration of the washed material due to the strength of the reagent. Permanent discoloration shows up after neutralization and washing with water since neutralization and water washing remove any temporary discoloration due to the treatment. On the other hand the temperature should not be so low as to render the acid inactive.

Unless certain precautions are observed, the addition of the neutralizing agent to th acid washed material may result in the formation of an emulsion.

I, therefore, prefer to add the neutralizing solution slowly and with moderate agitation, although alternate procedures may be employed.

Such alternate procedures include (a) the removal of the acid addition products by various solvents such as alcohol or glycerol before the alkali wash; (b) the addition of certain materials to the alkali wash such as liquid rosin, petroleum carboxylic acids, ethyl alcohol, oleic acid, and naphthenic acids; and (c) the addition of various emulsion inhibiting agents to the alkali wash such as aldehydes.

However, emulsions if formed can generally be broken by the addition of an absorbent material such as fullers earth followed by filtering or by the use of other suitable methods, such as electrical precipitation methods, the addition'of vari-- ous inorganic salts to the emulsion and the like.

Any other suitable neutralizing agent may be employed for the removal of excess acid and acid residues from the material under treatment. Examples of such neutralizing agents are lime, NazCOz, KOH, ammonia, fullers earth, clay and activated carbon.

These neutralizing agents may be applied in the solid form, or in the form of solutions in water or other solvent. They may be used alone or in combination with one or more other neutralizing agents, in which case they may be added to the treated solution together, or successively. For example, the acid-treated solution can be treated with clay to remove'the major portion of the acid and sludge present, the clay and adsorbed materials removed by filtration or by other suitable means, and solid NazCOa added to the solution to remove any residual acid or sludge present. Incidentally, this treatment usually serves to completely remove all of the water present in the treated solution, rendering unnecessary any further drying operations.

If desired, inertsolvents such as petroleum naphtha and carbon tetrachloride may be added to the material under treatment either before or during the treating process.

Such materials are usually added to reduce the loss of oleflnes and diolefines present, although they may have other functions.

The crude fractions which may be treated by my process may have any reasonable boiling range.

For instance, crude styrene fractions may have a b ilin range of from C. to C. or wider although I prefer to use crude styrene fractions with boiling rangeswhich do not greatly exceed from 140 C. to 150 0.

approximately 80% to 95% boils between 167 C. and 175 C. Likewise, a valuable indene fraction is obtained from light oil when approximately 80% to 95% boils between 177 C.and 186 C.

In general, and with all other conditions unchanged, the extent of purification will, generally speaking, be directl proportional to the'narrowness in boiling range of the starting material.

Results comparable to those particularly set I 'forth above in connection with styrene are obtained upon the polymerization of other light oil fractions such as methyl styrene and indene treated by my process. As an example a purified methyl styrene fraction may be polymerized by subjecting it to a ,temperature of 80 C. for a period of 8 days, followed by removal of unpolymerized material by vacuum distillation. -The polymerized material has a color of 0.0 (water white) on the Gardner color scale. p

Also as an example, a purified indene fraction maybe polymerized by adding it to a suspension of 2.0% by weight of ferric chloride in toluene, followed by stirring for a period of three hours. The catalyst is then hydrolyzed by the addition of the theoretical amount of sodium hydroxide in the form of a 20% solution. 'Ihemixture then is filtered and the unpolymerized material removed by steam distillation. The polymerized material has a color of 4.0 on the Gardner color scale.

Unwashed indene polymerized in a similar manner has a color of 8.0 on the Gardner color scale.

Crude styrene solutions containing any quantity of styrene such as from 1.0% to 99% may be refined by my method.

Excellent results are obtained with styrene solutions containing from-10% to 80% styrene.-

Comparable concentrations apply to the refinlng'of other unsaturated hydrocarbons.

Further examples of such other unsaturated hydrocarbons are the other olefines and diolefines obtained from light oil, from drip oil (from gas mains), from coal tar, from cracked distillates, and from synthetic or other sources.

Contact between the material undergoing treatment and the treating material, namely conjunction-with other neutralizing agents, such jaasaors the unsaturated-hydrocarbon, or fractions containing the unsaturated hydrocarbons with successive portions of the acid in order to effect a more thorough purification of the hydrocarbon solution, or. a more economical utilization of the acid mixture, or both. The batchwise addition of the acid mixture may be made with or without the removal of a portion or all of the acid and acid sludge from the preceding application and with or without additional refining steps. such as neutralization, drying, fractionation, and/or crystallization between successive batchwise additions of the acid refining agent.

In certain cases it may be found to be desirable to contact fresh charges of the unsaturated hydrocarbon fractions with spent acid and/or acid sludge and residues from the preceding refining step in order to secure greater economy in the use ofthe acid and/or a more thorough purification of the hydrocarbon fractions. The hydrocarbon fraction so treated may then be contacted with additional quantities of fresh acid, either with or without previously removing the acid sludge from the initial treatment and with or without additional refining steps, such as neutralization. drying, fractionation and/or distillation, and the refining operation completed in the normal manner, namely by separation of the respective layers, followed by neutralizing, drying, and/or distilling.

The'treated material, of course, lends itself to further purification, should this be desired. Such further purification may be by contact with clay,

with activated carbon, or with diatomaceous earth at any suitable temperature, or by distillation at any desired pressure, or by partial polymerization followed by removal of undesirable constituents, or by fractional crystallization, or by other physical or chemical means, or by any combination of these methods.

By operating my process more drastically it may be employed to completely remove the olefines and dioleflnes present in the material undergoing treatment leaving the aromatic hydrocarbons, naphthenes and/or parafiins unchanged. Special solvents may be prepared in this manner.

Other variations will become apparent to persons skilled in the art upon becoming familiar v with this invention.

The treating process as outlined in the example listed may be greatly simplified in most cases. For example, I find that styrene solutions may be refined in'a satisfactory manner by treatment with the acid solution, followed by the application of clay or activated carbon, either alone or in as sodium carbonate or lime, and the removal of all solid material from the treated solution by filtration or by other suitable means. No further treatment is usually necessary.

While the invention has been more particularly described in connection with ortho-phosphoric acid (H1PO4) it is to be understood that any other compound consisting of hydrogen phosphorus and oxygen or of phosphorus and oxygen might be substituted. For instance, pure P205 or any other phosphoric acid may be employed for generally speaking all phosphoric acids comprise solutions of P205 in water. Likewise, pure P203 or any phosphorous acid might be substituted. Generally speaking, all phosphorous acids comprise solutions of P203 in water. However, compounds such as H3PO4 (ortho-phosphoric acid), H4P2O'l (pyro-phosphoric acid), and HPOs (meta-phosphoric acid) are preferred.

The term "oxy-acid of phosphorus as used in the claims is intended to embrace the phosphoric acids, the phosphorous acids, the corresponding anhydrides, and mixtures of the foregoing.

The term permanent color as used in the claims is intended to mean color which remains after the removal of acid and acid reaction products such as by neutralization and water washing followed by distillation.

It is, therefore, to be understood that the above examples are by way of illustration and that changes, omissions, additions, substitutions, and/or modifications might be made within the scope of the claims without departing from the spirit of the invention which is intended to be limited only as required by the prior art.

I claim:

1. A process for preparing a refined solution of a resin-forming unsaturated light oil hydrocarbon which is highly resistant to color formation when subjected to conditions for the polymerization of said unsaturated hydrocarbon which comprises subjecting light oil produced in the manufacture of artificial gas to fractional distillation to obtain a relatively close out of said unsaturated hydrocarbon, treating said out with from 2% to by volume of acid selected from a group consisting of ortho-phosphoric acid, pyro-phosphoric acid and meta-phosphoric acid, said acid being from 60% to 90% in concentration, said treatment taking place at a temperature between 10 C. and 30 C. but sufiiciently low to avoid adding any appreciable permanent color to said hydrocarbon and to avoid polymerizing a large part of said hydrocarbon due to the strength of said acid, and then removing residual acid from said out.

2. A process for preparing a refined styrene out which comprises subjecting light oil produced in the manufacture of artificial gas to fractional distillation to obtain a cut the preponderate part of which boils between 142 C. and 148 C., treating said out with from 2% to 10% by volume of acid selected from a group consisting of ortho-phosphoric acid, pyro-phosphoric acid, and meta-phosphoric acid, said acid being from 60% to 90% in concentration, said treatment taking place at a temperature between --10 C. and 30 C. but sufllciently low to avoid adding any appreciable permanent color to said hydrocarbon and to avoid polymerizing a large part of said hydrocarbon due to the strength of said acid, and removing residual acid from said styrene cut.

3. A process for preparing a refined methyl styrene cut which comprises subjecting light oil produced in the manufacture of artificial gas to fractional distillation to obtain a cut the preponderate part 01' which boils between 167 C. and 175 C., treating said out with from 2% to 10% by volume of acid selected from a group consisting of ortho-pliosphoric acid, pyro-phosphoric acid and meta-phosphoric acid, said acid being from 60% to 90% in concentration, said treatment taking place at a temperature between -'-10 C. and 30 C. but sufliciently low to avoid adding any appreciable permanent color to said hydrocarbon and to avoid polymerizing a large part of said hydrocarbon due to the strength of said acid. and removing residual acid from said methyl styrene cut.

4. A process for preparing a refined indene out which comprises subjecting light oil pro duced in the manufacture of artificial, gas to fracticnai distillation to obtain a cut the pra ponderate part of which boils between 177 C. and 186 C., treating said out with from 2% to 10% by volume of acid selected from a group consisting of ortho-phosphoric acid, pyro-phosphoric acid and meta-phosphoric acid, said acid being from 60% to 90% in concentration, said treatment taking place at a temperature between -10 C. and C. but sufliciently low to avoid adding any appreciable permanent color to said hydrocarbon and to avoid polymerizing a large part of said hydrocarbon due to the strength of said acid, and removing residual acid from said indene cut.

5. A process for the purification of a particular resin-forming unsaturated hydrocarbon concentrated in a light oil fraction which comprises contacting said light oil fraction in the liquid phase with a reagent comprising oxy-acid of phosphorus at least 50% in concentration, said contact of said fraction and said reagent taking place at a temperature below 75 C. and under conditions including acid concentration and temvperature sufficiently drastic to remove color forming bodies but insufiiciently drastic to polymerize a large part of said resin-forming unsaturated hydrocarbon and insufliciently drastic to add any appreciable permanent color to said fraction, and removing said reagent from said fraction.

6. A process for preparing a refined cut of a resin-forming unsaturated light oil hydrocarbon which is highly resistant to color, formation when subjected to conditions for the polymerization of said unsaturated hydrocarbon which comprises subjecting light oil to fractional distillation to obtain a cut of said unsaturated hydrocarbon, treating said out in the liquid phase with from 0.2% to 50% by volume of oxy-acid of phosphorus, said acid being at least 50% in concentration, said treatment taking place at a temperature below 75 C. and under conditions including acid concentration and temperature suiiiciently drastic to remove color forming bodies but insufficiently drastic to polymerize a large part of said resin-forming unsaturated hydrocarbon and insufficiently drastic to add any appreciable permanent color to said out, and removing said reagent from said cut.

7. In a process for the purification of a resinforming unsaturated hydrocarbon derived from light oil, the steps of treating said hydrocarbon in the liquid phase with oxy-acid of phosphorus, said treatment taking place at a temperature below 75 C. and under conditions including acid concentration and temperature sufficiently drastic to remove color forming bodies but insufliciently drastic to polymerize a large part of said resin-forming unsaturated hydrocarbon and insufiiclently drastic to add any appreciable permanent color to said hydrocarbon, and removing said reagent from said hydrocarbon.

8. In a process for the purification of a resiniorming unsaturated hydrocarbon derived from light oil, the steps of treating said hydrocarbon in the liquid phase with phosphoric acid, said treatment taking place at a temperature below 75 C. and under conditions including acid concentration and temperature sufiiciently drastic to remove color forming bodies but insufficiently drastic to polymerize a large part of said resinforming unsaturated hydrocarbon and insufiiciently drastic to add any appreciable permanent color to said hydrocarbon, and removing said reagent from said hydrocarbon.

FRANK J. SODAY. 

